There is already known a tool for surfacing an optical surface that includes a rigid support having a transverse end surface, an elastically compressible interface that is pressed against and covers said end surface, and a flexible pad adapted to be pressed against the optical surface and that is pressed against and covers at least part of the interface on the opposite side of and in line with said end surface.
To reduce the roughness of the optical surface, the tool is brought into contact with the latter, maintaining sufficient pressure of the tool on it for the pad to espouse the shape of the optical surface through deformation of the interface.
While spraying the optical surface with a fluid, it is driven in rotation relative to the tool (or vice-versa) and it is swept by means of the latter.
It is generally the optical surface that is driven in rotation, its rubbing against the tool being sufficient to drive the latter in rotation conjointly.
The surfacing operation necessitates an abrasive which can be contained in the pad or in the fluid.
During surfacing, the elastically compressible interface compensates the curvature difference between the end surface of the support of the tool and the optical surface, so that the same tool is adapted to a range of optical surfaces with different curvatures and shapes.
French patent application 2 834 662, which corresponds to American patent application 2005/0101235, proposes a surfacing tool of this kind which, whilst being adapted to a sufficiently vast range of optical surfaces, in terms of curvatures (convexity, concavity) and shapes (spherical, toric, aspherical, progressive or any combination of the latter, or more generally “freeform”), has good stability during surfacing and provides reliable and fast surfacing of good quality.
One embodiment of the tool proposed by the above document is described hereinafter with reference to FIGS. 1 to 3 of the appended drawings, in which:
FIG. 1 is an exploded perspective view of this tool and an ophthalmic lens having an optical surface to be surfaced;
FIG. 2 is a view in section of this tool shown assembled, during surfacing of the optical surface of the lens from FIG. 1; and
FIG. 3 is a diagrammatic plan view representing this ophthalmic lens during surfacing by means of this tool, which is represented while sweeping the optical surface in two positions, one of which is shown in dashed line.
In FIG. 1 there is represented a tool 1 for surfacing an optical surface 2, in this instance one of the faces of an ophthalmic lens 3. In FIG. 1, as in FIG. 2, the optical surface 2 concerned is represented as concave, but it could equally well be convex.
The tool 1 is formed of a stack of at least three parts, namely a rigid part 4, an elastically compressible part 5, and a flexible part 6 which, hereinafter, will respectively be called the support, the interface and the pad.
As is apparent in FIG. 1 in particular, the support 4 includes two jaws, namely a lower jaw 7 and an upper jaw 8 adapted to be superposed and nested one in the other by way of a peg 9 projecting from one face 10 of the upper jaw 8, adapted to be accommodated in a complementary hole 11 formed facing it in a face 12 of the lower jaw 7.
As can be seen in FIG. 1, the support 4 is globally a cylinder with circular symmetry and has an axis of symmetry X that defines a longitudinal direction.
The normal to the optical surface 2 at the point of intersection of the axis of symmetry X of the tool 1 therewith is denoted n.
On the side opposite its face 12 in which the hole 11 is formed, the lower jaw 7 has an end surface 13 extended substantially transversely, against which the interface 5 is pressed, covering it.
The pad 6 is pressed against the interface 5 on the other side of the latter relative to the support 4.
More precisely, the pad 6 covers at least part of the interface 5 on the opposite side to and in line with the end surface 13.
The rubbing of the pad 6 against the optical surface 2 ensures, by means of an abrasive contained in the spray fluid or incorporated into the pad 6 itself, superficial removal of material on the optical surface 2 in order to modify the surface state, as will emerge hereinafter.
The pad has a central portion 6a that is in line with the end surface 13 and a peripheral portion 14 which is located transversely beyond the end surface 13.
This peripheral portion 14 is connected to the support 4 by spring return means 15.
The peripheral portion 14 is in line with the central portion 6a and, when at rest, is substantially coplanar with it.
In the example shown in FIGS. 1 and 2, the pad 6 is in one piece, the peripheral portion 14 being connected to the central portion 6a, so that they in fact form a single part.
In an embodiment represented in bold line in FIG. 1, the pad 6 is flower-shaped and thus comprises a plurality of petals 14b which, projecting transversely from the central portion 6a, form the peripheral portion 14 of the pad 6 and each extend transversely beyond the end surface 13.
In a variant represented in chain-dotted line in FIG. 1, the peripheral portion 14 is in the shape of a ring 14a that surrounds the central portion 6a. 
In this case, in the absence of any load, the pad 6, if it is in one piece, is in the shape of a disc of material whose thickness is small compared to its diameter, as shown in FIG. 1, the peripheral portion 14, 14a thus forming a flange relative to the end surface 13.
The return means 15, which will be described later, can be disposed directly between the support 4 and the peripheral portion 14 of the pad 6, i.e. in practice the flange 14a or the petals 14b. 
The interface 5 has not only a central portion 5a that is located in line with the end surface 13 but also a peripheral portion 16 that is transversely beyond the end surface 13.
This peripheral portion 16 is in line with the central portion 5a and, in the absence of any load, is in the shape of a ring that surrounds the central portion 5a, for example, and is in fact disposed between the peripheral portion 14 of the pad 6 and the return means 15.
As can be seen in FIGS. 1 and 2, the interface 5 is in one piece, its central portion 5a and peripheral portion 16 being in fact connected to form together a single part, the peripheral portion 16 forming a flange relative to the end surface 13.
Thus in the absence of any load the one-piece interface 5 is in the shape of a disc of material whose thickness is small compared to its transverse dimension (i.e. its diameter), for example.
When the interface 5 and the pad 6 are both in one piece, they have comparable transverse dimensions. In particular, when each is in the form of a disc of material, for constructive convenience they are preferably the same diameter. However, there could equally be provision for using a pad of different diameter to that of the interface, in particular a greater diameter in order to attenuate edge effects of the tool on the worked surface.
Moreover, for reasons that will become apparent hereinafter, a deformable ring 17 is provided, disposed between the peripheral portion 16 of the interface 5 and the return means 15.
In practice, this ring 17 is fixed to the peripheral portion 16 on the other side of the latter to the pad 6, i.e. on the same side as the support 4, and so that the latter is surrounded by the ring 17.
This ring 17 preferably has a circular longitudinal section, but it could equally have a section of more complex shape, in particular oblong, polygonal, rectangular or square shape. Moreover, it is disposed on the peripheral portion 16 concentrically with the support 4.
The return means 15 is described next.
It comprises at least one elastically flexible leaf 18 that projects transversely from the support 4 and is connected, on the one hand, rigidly, to the support 4 by a first end 18a and, on the other hand, to the peripheral portion 14 of the pad 6 by a second end 18b, called the free end, opposite the first end 18a. 
As a result, the effect of a force exerted longitudinally on the peripheral portion 14 in line with this leaf 18 is that the latter is deformed, exerting on the peripheral portion 14 a reaction opposite to said force.
In practice, the return means 15 include a plurality of such leaves 18, distributed uniformly at the periphery of the support 4, to act on the whole of the peripheral portion 14 of the pad 6.
The return means 15 in fact take the form of a star-shaped part 19 fixed rigidly to the support 4.
The star-shaped part 19 has a central portion 20 from which project a plurality of branches 18 each forming an elastically flexible leaf extended radially in a transverse plane.
For fixing the star-shaped part 19 to the support 4, its central portion 20 is in practice clamped between the jaws 7, 8 of the support 4, it being centered by means of a through-hole 21 produced at its center, through which passes the peg 9 of the upper jaw 8, the assembly being held by fixing means such as screws which, passing through the upper jaw 8 and the central portion 20 of the star-shaped part 19, are engaged in the lower jaw 7.
If, as in an embodiment previously described, the one-piece pad 6 has a plurality of petals 14b, there are provided on the star-shaped part 19 as many branches 18 as there are petals 14b, the star-shaped part 19 being oriented so that each branch 18 extends in line with a petal 14b. Thus if the pad 6 has seven petals 14b, the star-shaped part 19 has seven branches 18 each adapted to provide the return spring force for one petal 14b. 
The ring 17 is fixed to the interface 5, which fixing can be provided by any means, although gluing is preferred, in particular for its simplicity.
In the embodiment represented, the diameters of the interface 5, the pad 6 and the star-shaped part 19 have a value at least twice that of the diameter of the support 4.
Moreover, when it is a question of surfacing an ophthalmic lens, the diameters of the interface 5 and the pad 6 are chosen to be substantially equal to the diameter of the lens 3, with the result that the diameter of the support 4 is much less than the diameter of the lens 3.
The use of the tool 1 is illustrated in FIGS. 2 and 3.
In this instance it is a question of surfacing or grinding an aspherical convex face 2 of an ophthalmic lens.
The lens 3 is mounted on a rotary support (not shown) by means of which it is driven in rotation about a fixed axis Y.
The tool 1 is pressed against this face 2 with sufficient force for the pad 6 to espouse its shape. Here the tool 1 is free to rotate and off-center relative to the optical surface 2. Forced driving of the tool in rotation by appropriate means can nevertheless be provided.
The relative rubbing of the optical surface 2 and the pad 6 is sufficient to drive the tool 1 in rotation in the same direction as the lens 3 about an axis substantially coincident with the axis of symmetry X of the support 4.
The optical surface 2 is sprayed with a non-abrasive or abrasive spray fluid according to whether the pad exercises this function itself or not.
In order to sweep the whole of the optical surface 2, the tool 1 is moved during surfacing along a radial trajectory, the point of intersection of the rotation axis X of the tool 1 with the optical surface 2 effecting a to and fro movement between two turnaround points, namely an exterior turnaround point A and an interior turnaround point B both situated at a distance from the rotation axis Y of the lens 3.
The central portion 6a of the pad 6 is deformed to espouse the shape of the optical surface 2 thanks to the compressibility of the central portion 5a of the interface 5.
As for the peripheral portion 14 of the pad 6, it is deformed to espouse the shape of the optical surface 2 thanks to the deformation of the flexible leaves 18.
Given the rigidity of the support 4, material is removed for the most part in line with the end surface 13, i.e. this removal of material is effected essentially by the central portion 6a of the pad 6.
As for the peripheral portions 14 of the pad 6 and 16 of the interface 5, they have essentially a stabilizing role, on the one hand thanks to the increased span or seat of the tool 1 compared to a standard tool the pad and the interface whereof would be limited to the central portions 5a, 6a and, on the other hand, thanks to the return means 15 that maintain a permanent contact between the peripheral portion 14 of the pad 6 and the optical surface 2.
The deformable ring 17 smoothes the distribution of the load exerted on the peripheral perimeter of the interface 5 and therefore on the pad 6 by the leaves 18.
As a result of this, whatever the location of the tool 1 on the optical surface 2 and whatever its rotation speed, its rotation axis X is always colinear or substantially colinear with the normal n to the optical surface 2, the orientation of the tool 1 therefore being the optimum at all times.
In the embodiment shown in FIGS. 1 and 2, the end surface 13 of the support 4 is flat.
The tool 1 is therefore adapted to surface a certain range of optical surfaces 2 with different curvatures.
In order to modify the adaptability of the tool 1, it is possible to preload the return means 15 by twisting the flexible leaves 18 so that they are already flexed when no load is applied, one way or the other.
If when no load is applied the leaves 18 are straight or flexed away from the end surface 13, the tool 1 is intended for concave optical surfaces 2, whereas if when no load is applied the leaves 18 are flexed on the same side as the end surface 13 the tool 1 is intended for convex optical surfaces 2.
In a first variant that is not shown, the end surface 13 of the support 4 is convex, the tool 1 thus being intended for optical surfaces 2 having a more pronounced concavity.
In a second variant that is not shown, the end surface 13 of the support 4 is in contrast concave, the tool 1 thus being intended for optical surfaces 2 of more pronounced convexity.
Of course, it is possible to combine the concave or convex implementation of the end surface 13 with the preloading of the return means 15 as described hereinabove.
French patent application 2 857 610, which corresponds to the international application WO 2005/007340, proposes that the spring return means, rather than taking the form of a star-shaped part such as the part 19 shown in FIGS. 1 and 2, have a continuous peripheral portion cooperating in bearing fashion with the peripheral portion of the pad like the pad 6, directly or through the intermediary of the only interface such as the interface 5 (there is no deformable ring like the ring 17), the return spring means including, in addition to the continuous peripheral part, a flat or curved flange fixed rigidly on the inside to the support like the support 4, this flange being formed by a perforated or solid wall.
The continuous character of the peripheral portion of these return means increases the regularity of the surfacing effected by the tool.